JP3642105B2 - Battery pack - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery pack of a lithium ion battery.
[0002]
[Prior art]
There is a nickel cadmium battery as a rechargeable battery (secondary battery), and its charging characteristics are as shown in FIG. 3A. That is, when an empty nickel cadmium battery is charged with a constant direct current, the terminal voltage gradually increases as the battery is charged. When the battery is fully charged, the terminal voltage shows a maximum value, and then gradually decreases. Note that the terminal voltage decrease rate (rate) is about 10 to 20 mV / min when the charging current is 1 C.
[0003]
Therefore, when charging a nickel cadmium battery, the terminal voltage is checked while charging, and when the terminal voltage starts to drop, if the charging is stopped, the battery can be fully charged, and overcharging can be performed. Can be prevented.
[0004]
FIG. 4 shows an example of a charging apparatus that performs charging by such a method, wherein reference numeral 10 denotes the charging apparatus, and reference numeral 20 denotes a battery pack of a nickel cadmium battery.
[0005]
Then, a commercial AC voltage of, for example, 100 V from the power plug 11 is supplied to the power supply circuit (AC-DC converter) 12 to extract a predetermined DC voltage, and this DC voltage is supplied to the constant current circuit 13 to, for example, 1C A constant current I13 for charging having a magnitude of is formed. The constant current I13 is output to the positive charging terminal T11 through the charging control switch circuit 14 and further through the backflow preventing diode D11. Reference sign T12 is a negative charging terminal.
[0006]
A microcomputer 15 is provided for charge control, and an operating voltage is supplied from the power supply circuit 12 to the microcomputer 15. Further, the voltage obtained between the output side of the switch circuit 14 and the ground is divided by resistors R11 and R12, and the divided voltage V11 is an analog input port (A / D converter) of the microcomputer 15. Supplied to A / D. The output of the output port Q11 of the microcomputer 15 is supplied to the switch circuit 14 as its control signal. Reference numeral C11 is a capacitor for removing a noise component, a ripple component, and the like included in the voltage V11.
[0007]
On the other hand, in the battery pack 20, in this example, three nickel cadmium batteries 21A to 21C are connected in series, and thus the rated output voltage is 3.6V. Further, the capacity is set to, for example, 1000 mAh.
[0008]
The positive electrode of the battery 21A is connected to the positive charge / discharge terminal T21, and the negative electrode of the battery 21C is connected to the negative charge / discharge terminal T22 through the resistor R21 having a small value for current detection and the protection switch circuit 22. Connected to. During charging, terminals T21 and T22 of battery pack 20 are connected to terminals T11 and T12 of charging device 10, respectively.
[0009]
Further, the battery pack 20 is provided with a detection circuit 23, the terminal voltages of the batteries 21A to 21C are input as detection inputs, and the drop voltage generated in the resistor R21 is supplied as the detection input. It is supplied to the circuit 22 as a control signal.
[0010]
In such a configuration, when the battery pack 20 is connected to the charging device 10, the constant current I13 from the constant current circuit 13 is changed to the switch circuit 14, the diode D11, the terminal T11, the terminal T21, the batteries 21A to 21C, and the resistor. The battery flows from the R21 → switch circuit 22 → terminal T22 → terminal T12 → ground line, and the batteries 21A to 21C are charged with a constant current I13 having a magnitude of 1C.
[0011]
As the battery is charged, the terminal voltages of the batteries 21A to 21C increase as described above (as shown in FIG. 3A). At this time, the terminal voltages of the batteries 21A to 21C are divided by the resistors R11 and R12, and the divided voltage V11 is supplied to the microcomputer 15 to monitor the terminal voltages of the batteries 21A to 21C. .
[0012]
When the battery is fully charged, the terminal voltages of the batteries 21A to 21C become maximal and then decrease, but this is detected by the microcomputer 15 through the voltage V11, and the switch circuit 14 is turned off by the microcomputer 15 to charge the battery. Ends. Therefore, the batteries 21A to 21C are fully charged and are not overcharged.
[0013]
When charging, the voltage supplied to the batteries 21A to 21C becomes abnormally high due to some trouble, or when the charging current or discharging current (load current) of the batteries 21A to 21C becomes abnormally high, this is detected. Detected by the circuit 23, the switch circuit 22 is turned off by the detection output, and the batteries 21A to 21C are protected from an excessive voltage or an excessive current.
[0014]
[Problems to be solved by the invention]
By the way, a rechargeable battery pack is widely used as a power source for commercial portable electronic devices such as a VTR for coverage. However, the battery pack is generally a battery pack of a nickel cadmium battery as described above. Yes.
[0015]
On the other hand, in recent years, lithium ion batteries have been developed and put into practical use as rechargeable batteries. Since this lithium ion battery is light in capacity, it is extremely effective as a power source for a news gathering VTR.
[0016]
In other words, the lithium ion battery has a higher output voltage per unit than the nickel cadmium battery, and in the VTR for coverage, etc., the battery voltage is transformed by the built-in DC-DC converter. The possible time is 50% to 100% longer. For example, in the case of VTR coverage, 5-10 battery packs as described above are carried in order to ensure that a power source is obtained, but in the case of lithium ion batteries, the number is 30% to It can be reduced by 40%.
[0017]
Therefore, a battery pack using a lithium ion battery is extremely effective for business use.
[0018]
However, the charging characteristics of the lithium ion battery are as shown in FIG. 3B. In other words, this characteristic diagram shows a case where a lithium ion battery is charged at a constant current until the amount of charge reaches 50%, and thereafter charged at a constant voltage. In the case of a battery, the terminal voltage does not decrease even when the battery is fully charged.
[0019]
For this reason, if the charging device 10 which charges the battery pack 20 of the nickel cadmium battery described above is used to charge the battery pack of the lithium ion battery, the full charge cannot be detected and the battery is overcharged.
[0020]
The present invention is intended to solve the above problems and provide a battery pack of a lithium ion battery that can be appropriately charged by the charging device 10 that charges the battery pack 20 of the nickel cadmium battery. .
[0021]
[Means for Solving the Problems]
In this invention,
A pair of charge / discharge terminals;
A lithium-ion battery;
A first switch circuit connected in series between one electrode of the lithium ion battery and one of the pair of charge / discharge terminals;
A detection circuit for detecting a full charge of the lithium ion battery;
A resistor and a second switch circuit connected in series between the pair of charge / discharge terminals;
A control circuit for controlling the first switch circuit and the second switch circuit according to the detection output of the detection circuit;
When charging, the control circuit turns on the first switch circuit and controls the second switch circuit off,
When the detection circuit detects a full charge of the lithium ion battery, the control circuit controls the first switch circuit to be turned on / off at a predetermined cycle, and the second switch circuit is set to the first switch. On / off control contrary to the switch circuit, and
Among the on / off cycles of the first switch circuit, a battery pack in which the on-period ratio is lengthened to gradually decrease the voltage between the pair of charge / discharge terminals. is there.
[0022]
As a result, compatibility with the battery pack of the nickel cadmium battery is ensured even during charging.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
1, reference numeral 30 denotes a battery pack according to the present invention. In this example, the battery pack is configured to be charged by the charging device 10 described in FIG. 4. Therefore, one lithium ion battery 31 is used. Have The positive electrode of the battery 31 is connected to the positive charge / discharge terminal T31, and the negative electrode is connected to the negative charge / discharge terminal through the resistor R31 having a small value for current detection and the switch circuit 32 for battery protection. Connected to T32.
[0024]
In addition, an overvoltage and overcurrent detection circuit 33 is provided, the terminal voltage of the battery 31 is supplied to the detection circuit 33, and the voltage drop generated in the resistor R31 is supplied to the detection circuit 33.
[0025]
Furthermore, a detection circuit 34 that detects the terminal voltage of the battery 31 is provided. The detection circuit 34 detects a full charge from a rise in terminal voltage when the battery 31 is charged with a constant current. In this example, the detection circuit 34 detects when the terminal voltage reaches 4.3V. It is. The detection outputs of the detection circuits 33 and 34 are supplied to the control circuit 35, and the output signal S35 of the control circuit 35 is supplied to the switch circuit 32 as its control signal. The switch circuit 32 is turned on when the control signal S35 is "0" and turned off when the control signal S35 is "1".
[0026]
Further, the switch circuit 36 and the resistor R32 are connected in series between the terminal T31 and the terminal T32, and the series circuit of the resistor R33 and the switch circuit 37 is connected in parallel to the battery 31. Then, the output signal S35 of the control circuit 35 is supplied to the inverter circuit 38 to obtain a signal whose level is inverted, and this inverted signal is supplied to the switch circuits 36 and 37.
[0027]
In this case, the resistor R32 is set to a value corresponding to the operation described later, and the resistor R33 is set to a value such that the battery 31 flows a discharge current of about 0.1 C to 0.2 C, for example, when the switch circuit 37 is on. Is done. The switch circuits 36 and 37 are turned off when the control signal S35 is "0" and turned on when "1".
[0028]
Further, the battery pack 30 is charged by the charging device 10 described with reference to FIG. 4, and the output voltage of the charging device 10 when no load is applied is the rated output voltage 3.6V of the battery pack 20 of the nickel cadmium battery of FIG. It is assumed that the voltage is doubled 7.2V.
[0029]
Further, in the charging device 10 of FIG. 4, when the battery pack 20 is not connected, the voltage between the terminal T11 and the terminal T12 becomes the above-mentioned no-load voltage 7.2V, and the battery pack 20 is connected. However, the voltage difference is notified to the microcomputer 15 by the divided voltage V11, and the microcomputer 15 determines whether or not the terminals T11 and T12 are unloaded. Suppose that it comes to detect.
[0030]
In such a configuration, at the time of steady operation, the control signal S35 is “0” as shown before time t1 in FIG. 2A, so that the switch circuit 32 is on as shown in FIG. As shown, the switch circuits 36 and 37 are off.
[0031]
Therefore, when the battery pack 30 is connected to the charging device 10, the constant current I13 from the constant current circuit 13 is changed from the switch circuit 14 → diode D11 → terminal T11 → terminal T31 → battery 31 → resistor R31 → switch circuit 32 → The battery 3 is charged with a constant current I13 having a magnitude of 1C through a line of terminal T32 → terminal T12 → ground.
[0032]
As this charging is performed, the terminal voltage of the battery 31 increases as shown in FIG. 3B. Correspondingly, as shown by the solid line in FIG. 2D, the voltage V30 between the terminals T31 and T32 is shown. Will also rise. In the following description, for the sake of simplicity, the voltage drop in the resistor R31 when operating normally is small and ignored, and the terminal voltage of the battery 31 and the voltage V30 are assumed to be equal.
[0033]
When the battery 31 is fully charged at time t1, that is, as shown by the solid line in FIG. 2D, when the terminal voltage of the battery 31 reaches the specified value 4.3V, this is detected by the detection circuit 34 and is sent to the control circuit 35. Be notified.
[0034]
Then, as shown in FIG. 2A, from time t1, the signal S35 is a pulse with a period τ of, for example, 20 milliseconds, and its duty ratio (ratio of “1” period) starts from 90%, for example, 15 minutes. It will be reduced by 10% so that it will be 10% later.
[0035]
In the period τ of the period τ, the switch circuit 32 is turned off and the switch circuits 36 and 37 are turned on, so that the battery 31 is not charged and the charging device 10 Charging current (constant current) I13 flows through the resistor R32. As a result, by setting the value of the resistor R32 in advance, the voltage V30 becomes, for example, 5V as shown by a solid line in FIG. 2D.
[0036]
In the period τ of the period τ, the switch circuit 32 is turned on and the switch circuits 36 and 37 are turned off during the period of S35 = "0". Therefore, the voltage V30 at the terminals T31 and T32 is shown by a solid line in FIG. As shown, the terminal voltage of the battery 31, that is, the specified value is 4.3V.
[0037]
Therefore, as shown by the solid line in FIG. 2D, the voltage V30 at the terminals T31 and T32 changes in a pulse shape corresponding to the signal S35 from the time point t1, and a high period of the voltage V30 corresponding to the duty ratio of the signal S35. The proportion of is gradually getting smaller.
[0038]
In the period τ, the switch circuit 32 is turned on and the switch circuits 36 and 37 are turned off during the period S35 = “0”, so that the battery 31 is charged even after full charge. In the subsequent period of S35 = "1", the switch circuit 37 is turned on and the battery 31 is discharged through the resistor R33 at a magnitude of 0.1 C to 0.2 C, for example, so that the battery 31 is overcharged. Absent.
[0039]
When the voltage V30 changes from the time t1 as shown by a solid line in FIG. 2D, the average voltage gradually decreases as shown by a broken line in FIG. 2D.
[0040]
When the average value of the voltage V30 decreases in this way, this is equivalent to the decrease in the terminal voltage after full charge in FIG. It is determined that the pack 30 is fully charged, and the switch circuit 14 is turned off.
[0041]
Therefore, the charging of the battery pack 30 is finished, and at this time, the battery 31 is fully charged.
[0042]
When the voltage supplied to the battery 31 becomes abnormally high due to some trouble during charging, or when the charging current or discharging current (load current) of the battery 31 becomes abnormally large, this is detected by the detection circuit 33. Then, the control circuit 35 is notified, the switch circuit 32 is turned off by the signal S35, and the battery 31 is protected from an excessive voltage or an excessive current.
[0043]
As described above, according to the battery pack 30 of FIG. 1, since the terminal voltage drop after full charge is generated in a pseudo manner, even if the battery pack 30 is a lithium ion battery pack, nickel cadmium is used. The charging device 10 for charging the battery pack can be fully charged and is not overcharged.
[0044]
According to the experiment, when 1C = 1000 mA under the above numerical conditions, the decrease in the average value of the voltage V30 after time t1 was 37.3 mV / min, and the charging could be terminated after about 2 minutes.
[0045]
If a nickel cadmium battery that has been left uncharged for a long time is charged, the terminal voltage decreases at the start of the charge, so for example, the decrease in the terminal voltage is ignored for 5 minutes from the start of charging. There is also a charging device. Therefore, in the battery pack 30 as well, after 5 minutes from the start of charging, that is, when a period of ignoring the decrease in the terminal voltage has elapsed, the processing after time t1 may be permitted.
[0046]
In addition, the direction of the current flowing through the resistor R31 is reversed between charging and discharging, and the polarity of the drop voltage generated in the resistor R31 is reversed, so that the detection circuit 33 detects an overvoltage using this. You can also change the voltage level.
[0047]
Further, when charging, if the voltage level at which the detection circuit 34 detects full charge is set in consideration of the voltage drop in the resistor R31 and the internal resistance of the battery 31, more reliable charging can be performed.
[0048]
【The invention's effect】
According to the battery pack of the lithium ion battery of the present invention, even when charging, the battery pack is compatible with the nickel cadmium battery, and even if it is a charging device that charges the battery pack of the nickel cadmium battery, it can be charged without excess or deficiency. it can. This also eliminates the need to purchase a new charging device for the battery pack of the lithium ion battery.
[Brief description of the drawings]
FIG. 1 is a connection diagram illustrating one embodiment of the present invention.
FIG. 2 is a waveform diagram showing an operation of the circuit of FIG.
FIG. 3 is a diagram showing charging characteristics of a rechargeable battery.
FIG. 4 is a connection diagram illustrating an example of a charging device and a rechargeable battery pack.
[Explanation of symbols]
30 = battery pack, 31 = lithium ion battery, 32 = switch circuit, 33 = detection circuit, 34 = detection circuit, 35 = control circuit, 36 = switch circuit, 37 = switch circuit, 38 = inverter circuit, T31 = + side Charge / discharge terminal, T32 = -side charge / discharge terminal

Claims (5)

A pair of charge / discharge terminals;
A lithium-ion battery;
A first switch circuit connected in series between one electrode of the lithium ion battery and one of the pair of charge / discharge terminals;
When the terminal voltage of the lithium ion battery rises to a fully charged voltage due to charging, a detection circuit that detects that the voltage has risen to the fully charged voltage ;
A resistor and a second switch circuit connected in series between the pair of charge / discharge terminals;
A control circuit for controlling the first switch circuit and the second switch circuit according to the detection output of the detection circuit;
When charging, the control circuit turns on the first switch circuit and controls the second switch circuit off,
The detection circuit, when the terminal voltage of the lithium ion battery is detected that rises to the voltage of the fully charged above, by the control circuit, which controls on and off the first switching circuit at a predetermined period, The second switch circuit is turned on / off in the opposite direction to the first switch circuit, and
A battery pack in which an on-off period of the first switch circuit is gradually lengthened so that an average voltage between the pair of charge / discharge terminals is gradually decreased. The battery pack according to claim 1,
During the period when the first switch circuit is off and the second switch circuit is on, the voltage between the pair of charge / discharge terminals is set higher than the full charge voltage detected by the detection circuit. A battery pack designed to be used. The battery pack according to claim 2,
A series circuit of another resistor and a third switch circuit is connected in parallel to the lithium ion battery,
A battery pack that is turned on / off simultaneously with the turning on / off of the second switch circuit. The battery pack according to claim 2,
A battery pack in which the processing of the control circuit is not executed for a predetermined period from the start of charging. The battery pack according to claim 2,
A battery pack configured to set a detection level of the detection circuit by correcting a voltage drop generated in an internal resistance of the lithium ion battery.

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